Wednesday, August 7, 2013

Book Review: Chemistry, Quantum Mechanics, and Reductionism by Hans Primas

Well, with a title like that, how can you go wrong? In this book, Hans Primas walks the line between physics-chemistry-mathematics and philosophy. Sections involving advanced mechanics algebra are outside of my field and it's not my field to critique those, but I found this fascinating. Two quotes by Goethe in a physical chemistry text is two more than what I've seen before, and there are other parallels I could make to Owen Barfield's arguments at times. Also, frequently Polanyi comes to mind. This book is as much philosophy as it is physical chemistry. Natural philosophy, of course.

Primas argues that it is not a trivial thing to cross from the quantum physical world to the classical physical world, and that some of the ways we "bridge the gap" mathematically don't work. To do it right, he starts from the ground up with a non-Boolean quantum logic that allows for superposition of states and also for the influence of the environment/measurement on the experiment. The biggest experimental indication that we need to do this seems to be the EPR correlations, which Primas argues shows that experiments are not as separable as we assume. I think I agree but am not enitrely convinced that EPR correlations affect classical outcomes.

Primas argues that we cannot so easily separate the experiment from the experimenter, and that we cannot build a classical physics from quantum mechanics alone. The extra ingredient we need to do so is context or observation on a classical level. Classical properties like chirality and molecular structure constrain the quantum mechanics. The world cannot be added up from quantum mechanics alone with a big enough computer, in other words.

What impressed me was the depth of philosophical thought. Primas is searching for a quantum ontology (if that's the right way to say it), and is not content with the standard "it's just what we measure, let's not think about what it means" Copenhagen interpretation. He digs back to Greek philosophy and makes the connections between his ideas and history as well as experiment and theory. He put his thoughts in the proper context, just like he argues we should do with our experiments.

It's strange to be reading a typed set of lectures from the 80's, but it worked for me, just like reading Polanyi's seminal article on similar topics still works. I found Primas by talking to Robert Bishop (philosophy of science, Wheaton) and reading his article "Whence Chemistry?" published in 2010, so people are still thinking about it, and it's not clear that Primas's objections have been adequately answered in the two decades since publication.

I'd like to list here for reference the six limits Robert mentioned to me that Primas lists, which must be crossed when moving from quantum to classical physics (p. 332ff). These are where the rubber meets the road for Primas's ideas, so they are particularly important:
1.) Shadow edges
2.) The van Hove limit
3.) The Boltzmann-Grad limit
4.) The Brownian-motion limit
5.) The Hartree limit
6.) Molecular structure (e.g., chirality)

I did not expect to get as involved in this book as I did, but it was a fascinating if somewhat vertiginous trip. Still processing and probably will be for quite some time.

PS: One useful tidbit: I did not know, or I knew but then forgot, that the Uncertainty Principle is not only found in Quantum Mechanics, but instead originated in the classical world. It's a consequence of limits on data transmittal, and in fact Heisenberg may have gotten the idea from a classical origin! So one of the prime examples of quantum weirdness actually doesn't require quanta.

PPS: As I was reading this a philosopher of science ran a pair of articles on the NYT philsophy blog about how he's frustrated at people who abuse quantum mechanics to make weird philosophical statements. I agree with him on many points but find his argument ultimately a lot less convincing on what really matters than the arguments of Primas. In fact, Primas argues forcefully against some of the statements made on that blog. Mostly, I'm frustrated with the attitude that if some people do the philosophy wrong, then EVERYONE must be doing the philosophy wrong and we all should just bite the bullet of the Copenhagen interpretation (or worse yet the Everett Many-Worlds interpretation). This is not a subject that can be resolved on a blog. Therefore ... I will shut up now!

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